The present invention relates to an audio channel system and, more particularly, to an audio channel system for outputting an analog signal corresponding to a sound waveform in a personal computer system by using shared processing elements.
Many prior art personal computers typically have high quality graphics, but do not always have high quality audio systems. The prior art audio systems tend to be somewhat simple in structure and produce tinny synthesized audio outputs.
Since computers cannot store analog waveform information, computer production of a sound must be represented as a finite string of digital signals. The time axis of a single sound waveform is divided into equal segments, each of which represents a small segment of time so that the waveform remains essentially stable. Each resulting segment is called an audio data sample. The samples are stored in the memory of the computer and can be played at any desired frequency. The computer feeds each sample to a digital to analog converter which changes the data sample into an analog voltage waveform which is then transmitted to an amplifier and a loud speaker. Frequently, the audio system comprises a small number of audio channels which are evenly divided between a left audio channel and a right audio channel. Each audio channel is usually programmed independently of the other audio channels and processed by separate audio processors. Since the audio processors may not always be perfectly synchronized with one another, this can cause malfunction (so called "glitches") in the audio output which result in poor sound quality. A "glitch" occurs when an undesired transient voltage spike occurs as a signal is being processed.
It would be advantageous for a computer to have an audio system which produces compact disc (CD) quality sound and in which each audio channel is processed synchronously using a shared processing element to produce high performance sound quality. In order for an audio system to produce CD quality sound, it must operate at a minimum sampling frequency of 44 KHz, which requires that the sound waveform to be played be processed quickly in order to achieve the desired sampling frequency.
The present invention is directed to an audio channel system for outputting an analog signal corresponding to a sound waveform in a personal computer system. The audio system includes eight audio channels, each of which is capable of producing a sound waveform comprising a predetermined number of audio data samples. Each audio channel is capable of being directed to a left audio channel, a right audio channel, both audio channels or neither audio channel. Each audio channel is pipelined serially into a single audio processing loop or shared processing element. A retiming RAM fine adjusts each data sample which is to be outputted. A pair of digital to analog converters direct the data samples to the appropriate channel. The data signals may also be outputted via a digital output shift register. The left and right digital audio values are also output via a digital shift register.